Method for isolating aleurone particles

ABSTRACT

The invention relates to a method and device for separating a mixture made of particles of a first particle type and a second particle type, especially aleurone particles and shell particles made of comminuted bran, said particles being scarcely distinguishable in terms of size and density, into various types of particles. Separation occurs according to particle-type specific triboelectric charging of said particles in a first active area and subsequent separation of the differently charged moving particles in an electric field.

This is a continuation application of Ser. No. 12/143,109, filed on Jun.20, 2008 now U.S. Pat. No. 7,641,134, which is a divisional applicationof Ser. No. 10/494,847, filed on Dec. 3, 2004 now U.S. Pat. No.7,431,228, which claims priority from International Application No.PCT/CH02/00547, filed Oct. 2, 2002, which claims priority from GermanApplication No. 101 54 462.6, filed Nov. 8, 2001, the completedisclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The invention relates to a method and a device for separating thevarious sorts of particles in a mixture comprised of particles producedby comminuting the grains of cereal grains, in particular wheat, and arepresent as a mixture consisting of at least first and second sort ofparticle. In addition, the invention relates to a product which is alsoobtained via the method and device according to the invention.

b) Description of the Related Art

WO 85/04349 describes a method for obtaining aleurone cell particlesfrom wheat grain. In this case, the grain particles are comminuted in ahammer mill in a first step, so that aleurone cell particles and shellparticles are present as a mixture. This mixture is given an electricalcharge through exposure to frictional electricity in a second step,wherein the aleurone cell particles and the shell particles receivedifferent electrostatic charges. In a third step, the mixture with thedifferently charged particles is moved through an electrical field, sothat the differently charged particles are varyingly deflected, whereinthe shell particles and aleurone cell particles are caught in separatecontainers. The frictional electric charge (step 2) takes place in astream of dry air, into which the mixture is introduced, and which movesin a hollow column. In this case, obviously turbulent air streams arisein the column (“elutriator”), wherein the particles in the mixture rubagainst both each other and the interior wall of the elutriator, therebyreceiving the respective electrostatic charge.

In this method of prior art, however, large quantities of air had to bemoved. Nonetheless, no intensive frictional electric interaction takesplace between the particles and the interior elutriator walls.

OBJECT AND SUMMARY OF THE INVENTION

Therefore, the primary object of the invention is to separate a mixturecomprised of various sorts of particles, in particular aleurone andshell particles from comminuted grain, which hardly differ in terms ofsize and density, into its various sorts of particles more efficientlythan in prior art.

This object is achieved by a method in which:

-   (a) The particles of the first particle sort and second particle    sort in the mixture are moved along at least one surface of at least    one solid material in a first impact area in such a way as that at    least one portion of their particle surface is at least sectionally    in contact with the solid material surface as they move along the at    least one solid material surface, as a result of which the particles    of the first particle sort and the particles of the second particle    sort become electrically charged in such a way that the electrical    charge of the particles of the first particle sort differs from the    electrical charge of the particles of the second particle sort    enough to enable an electrostatic separation of particles of the    first particle sort from particles of the second particle sort;-   b) in a second impact area, the particles of the first particle sort    and second particle sort with the sufficiently different electrical    charges are subsequently moved into an electrical field between a    first electrode area and a second electrode area, between which    there is an electrical potential difference, at essentially the same    velocity, as a result of which the particles of the first particle    sort and second particle sort with the sufficiently different    electrical charges move along sufficiently different paths as they    travel through the electrical field; and-   c) the particles of the first particle sort and the particles of the    second particle sort are caught at a first location and at a second    location at the end of their journey through the electrical field,    characterized in that the at least one surface of the at least one    solid material is concave in the first impact area, and that the    particles of the first sort and particles of the second sort in the    mixture moving along the concave surface are pressed against the    concave surface of the solid material as a result of their    centrifugal force as they move inside the first impact area.

The particles can be gathered at this first and second location, andremoved after enough have accumulated. As an alternative, they can alsobe continuously, e.g., pneumatically, conveyed further in step c) afterseparation in step b), and then be routed to a packaging system, forexample.

In particular, the particles of the first particle sort are aleuroneparticles, and the particles of the second particle sort are residualparticles from which aleurone has been removed, in particular shellparticles, of the comminuted grain.

The object according to the invention is also achieved with a the deviceaccording to the invention, with:

-   a) a first impact area with at least one surface of at least one    solid material, along which the particles of the first particle sort    and the second particle sort of the mixture can move in such a way    that at least one portion of their particle surface is at least    sectionally in contact with the solid material surface as they move    along the at least one solid material surface; and-   b) a second impact area subsequent to the first impact area, with a    first electrode area and a second electrode area, between which an    electrical voltage can be applied; and with a first accumulation    area for particles of the first sort and an accumulation area for    particles of the second sort separate from the first accumulation    area, characterized in that the at least one surface of the at least    one solid material is concave in the first impact area, so that the    particles of the first sort and second sort that can move along the    concave surface are pressed against the concave surface of the solid    material as a result of their centrifugal force as they move inside    the first impact area.

In particular, the at least one surface of the at least one solidmaterial is concave in the first impact area, so that the particles ofthe first sort and second sort that can move along the concave surfaceare pressed against the concave surface of the solid material as aresult of their centrifugal force as they move inside the first impactarea.

The product according to the invention, in particular aleuroneparticles, which was obtained by separating the various particle sortsof the mixture through the use of steps a), b), and c) of theaforementioned method, has a high level of purity.

It is preferably obtained through the repeated application of steps a),b), and c).

Additional advantages, features and possible applications of theinvention the following description of two exemplary embodiments of theinvention based on the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a first exemplary embodiment of the invention; and

FIG. 2 shows a second exemplary embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first device according to the invention as shown on FIG. 1 comprisesa supply vessel 22 in which the mixture 1 to be separated, whichcontains at least a first particle sort 2 and a second particle sort 3,is routed to the first impact area 13, 14, in which particles 2, 3 ofmixture 1 are given an electrical charge varying by particle sort beforethe particles 2, 3 carrying different electric charges are supplied tothe second treatment area 31, 32, 35, where they accumulate at differentlocations 33, 34 in a separation vessel 35, sorted according to type ofparticle based on their electric charge.

Through the force of gravity, the mixture 1 goes out of the feed vessel22, which tapers toward the bottom, into a conveyor device 18, 19consisting of a conveyor screw 18 and into a conveyor channel 19. Theconveyor screw 18, which is driven by a drive motor 23, conveys themixture 1 through a product inlet 15 into a housing 14, where a rotorelement 13 is rotatably mounted.

There is a gap area 21 between the rotor element 13, which is driven bya drive motor 24, and the housing 14, such that the mixture 1, which issupplied through the product inlet 15 and strikes the rotor element 13,is accelerated both radially and tangentially through this gap area dueto friction at the surface of the rotor element. The mixture 1accelerated in this way passes through the gap area 21 and obliquelystrikes the surface 11 of the inside wall of the housing, which has aconcave curvature. Due to its own inertia (centrifugal force) and due toconstantly resupplied mixture, the mixture 1 is pressed against thesurface 11 having a concave curvature and is conveyed along this surfaceuntil it comes out of the housing 14 through the product outlet 16 andenters a separation vessel 35.

The disk-shaped rotor element 13 has elevations 20, which are situatedon its disk surface facing the product inlet 15. In addition to theabove-mentioned friction on the surface of the rotor element 13 (“baffledisk”), these elevations 20 also contribute toward the acceleration ofthe mixture 1 and the ever-present air through the gap area 21, and onthe other hand, they also exert an impact effect (baffle effect) on theparticles 2, 3 of the mixture, so that any agglomerates of multipleparticles which might be present are broken up. This impact separation(baffle separation) of agglomerates before or during the buildup ofelectric charge on the particles due to friction on the solid bodysurfaces is important, because such agglomerates may of course alsoconsist of particles of different types, which would then reach thecollecting site 33 or at the collecting site 34, depending on theirtotal charge. Then, however, in any case one would have “foreignparticles” at the respective collecting sites 33 and 34.

Depending on their geometric shapes, these elevations 20 may haveprimarily an accelerating and/or pumping effect on the mixture and/orthe air, or they may have primarily a dispersing effect on the particlesof the mixture. A blocky, angular shape of these elevations 20 promotesa dispersing effect, while a paddle shape increases the acceleration orpumping effect. Elevations of different shapes may also be provided onthe rotor element 13 to achieve a controlled effect.

To prevent the mixture 1, which is supplied through the product inlet15, from traveling even a very short distance through the gap area 21between the product inlet 15 and the product outlet 16 and therebyescaping the necessarily intense action in the first treatment area 13,14, the product inlet 15 is situated eccentrically with respect to therotor element 13. In addition (and not for reasons of betterillustration as in FIG. 1), the product inlet 15 is situated directlybehind the product outlet 16 in the direction of rotation of the rotorelement 13 peripherally, so that the mixture travels at leastapproximately 360° on a spiral pathway in the gap area 21 between theproduct inlet 15 and the product outlet 16. This prevents“short-circuiting” of the pathway of the mixture between the productinlet and the product outlet.

During its path through the gap area 21, the particles 2, 3 of themixture 1 come in intense contact with the inside surfaces 11, 12 of thehousing 14 and with the surface of the rotor element 13, in particularits elevations 20 and the concave curvature of the inside surface 11 ofhousing 14. This leads to a specific electric charge buildup on theparticles of the different types of particles 2, 3.

Because of their high velocity, the dispersed particles coming outthrough the product outlet 6 go approximately horizontally into theseparation vessel 35, whereby the cylindrical neck area 35 a of theseparation vessel serves as a calming zone for the particles carryingdifferent electric charges as they come out of the housing 14. They thensettle out in the interior of the separation vessel under the influenceof gravity. In the interior of the separation vessel 35, there is afirst electrode 31 and a second electrode 32 opposite it. The firstelectrode 31 is grounded by a line 38, which contains a voltage source37, while the second electrode 32 is grounded directly via a line 39.The differently charged particles settling out in the electric fieldbetween the two electrodes 31 and 32 travel downward on different paths,depending on their electric charge. A partition 36, which projects fromthe bottom area 35 b of the collecting vessel 35 into the electric fieldbetween the electrodes 31, 32 subdivides the lower interior space of theseparation vessel 35 into a first collecting area 33 and a secondcollecting area 34 in which the particles of the first type and/or theparticles of the second type are collected.

In an advantageous modification of this first exemplary embodiment fromFIG. 1, an air classification is also performed in the first treatmentarea 13, 14. To this end, air or another gas mixture is pumped throughan air inlet (not shown) into the first treatment area 13, 14 and isguided within the first treatment area 13, 14 so that the fines (“flour”from endosperm residues, optionally still adhering to the aleuroneparticles) are separated from the coarse fraction (pure aleuroneparticles and pure husk particles), the fines being removed with the airstream through an air outlet (not shown) and only the coarse fractionpassing through the product outlet 16 into the second treatment area 31,32, 35.

The second device according to this invention as shown in FIG. 2 differsfrom that shown in FIG. 1 in its first treatment area. Otherwise all theelements are identical and carry the same reference notation as those inFIG. 1. Instead of the housing 14 with the rotor element 13 which isrotatably mounted on it and can be driven by the drive motor 24, thedevice in FIG. 2 has a curved channel with a first end 27 a and a secondend 27 b. The mixture 1 coming from a feed vessel 22, in particularaleurone particles and husk particles of the bran, is supplied through aproduct inlet 15, and a moving fluid, in particular air, is suppliedthrough a fluid inlet 29 to a fluidization area 17 at the end of whichthere is a dispersion angle 26, which is connected to the first end 27 aof the curved channel 27 and through which the fluidization area 17opens into the curved channel 27. The second end 27 b of the curvedchannel 27 opens into a product separator 28 with a fluid outlet 30 anda product outlet 16, which opens into the separation vessel 35.

The conveyor device 18, 19 transports the mixture 1 out of the feedvessel 22, through the product inlet 15 and into the fluidization area17. A sufficient amount of fluid at a sufficient velocity is used toachieve airborne conveyance without any accumulation of particles in theinterior of the curved channel 27. Due to the abrupt deflection when theparticles impact on the dispersing angle 26, the above-mentioneddispersion/de-agglomeration of the particles of the mixture isaccomplished. During their subsequent movement in the fluid stream anddue to the friction between the particles moving along the insidesurface of the curved channel 27, there is a particle type-specificbuildup of electric charge on the particle types 2, 3 of mixture 1. Thefluid is separated through the fluid outlet 30 in the downstream productseparator 28, and the mixture of the differently charged particlesaccording to type of particle then enters the separation vessel with itselectric field.

In principle, two cases of electric charging of the particles can bedifferentiated:

The particles of the first type of particle are negatively (positively)charged and the particles of the second type of particle are negatively(positively) charged, but to a different extent. These particles thusdiffer only in the absolute value of their charge, but not in thepolarity of the charge.

The particles of the first type of particle are negatively (positively)charged and the particles of the second type of particle are positively(negatively) charged. The particles thus differ in polarity and possiblyalso in the absolute value of their charge.

In the first case, the electrically charged particles of the first typeand those of the second type repel one another, and there is practicallyno re-agglomeration of different particles. Separation takes place inthe electric field due to different amounts of deflection in the samedirection.

In the second case, the electrically charged particles of the first typeand those of the second type attract one another and re-agglomeration ofdifferent particles is possible. Separation takes place in the electricfield due to different amounts of deflection in opposite directions.

To prevent re-agglomeration of particles in any case before they areseparated into the different types of particles in the electric field,the “particle densities” must be kept low and the “particle dwell times”must be kept short during the buildup of electric charge in the firsttreatment area accordingly.

In the first exemplary embodiment in FIG. 1, this is accomplishedbecause of the selected geometry due to the cross section of the gaparea, which becomes wider in the radial direction, and due to asufficiently high rotational speed of the rotor element 13.

In the second exemplary embodiment in FIG. 2, this is accomplished byadjusting a sufficiently low product throughput/fluid throughput ratioin the fluidization area 17 and a sufficiently high fluid velocity.

In all the exemplary embodiments of the device according to thisinvention, the type of particle and the type of solid material on whichthe particles develop a triboelectric charge play a significant rolewhether the first case or the second case is obtained.

Thus, for example, very good charge buildup and separation results wouldbe achieved for an aleurone particle/husk particle mixture if the solidsurfaces 11 and 12, which play a crucial role in the charge buildup, aremade of stainless steel.

While the foregoing description and drawings represent the presentinvention, it will be obvious to those skilled in the art that variouschanges may be made therein without departing from the true spirit andscope of the present invention.

LIST OF REFERENCE NOTATION

-   1 mixture of particles-   2 first type of particle-   3 second type of particle-   11 first surface (concave)-   12 additional surface-   13, 14 first treatment area (first exemplary embodiment)-   13 rotor element-   14 housing-   15 product inlet-   16 product outlet-   17 fluidization area-   18, 19 conveyor device-   18 conveyor screw-   19 conveyor channel-   20 elevation (baffle element, paddle element, . . . )-   21 gap area-   22 feed vessel-   23 drive motor (for conveyor screw)-   24 drive motor (for rotor element)-   26 dispersing angle-   27, 28 first treatment area (second exemplary embodiment)-   27 curved channel-   27 a first end of 27-   27 b second end of 27-   28 product separator-   29 fluid inlet-   30 fluid outlet-   31, 32, 35 second treatment area (first or second exemplary    embodiment)-   31 first electrode area-   32 second electrode area-   33 first location/collecting area-   34 second location/collecting area-   35 separation vessel-   35 a neck area-   35 b bottom area-   36 partition-   37 voltage source-   38, 39 electric lines

1. A device for separating the various sorts of particles in a mixturecomprised of particles produced by comminuting the grains of cerealgrains, in particular wheat, and are present as a mixture consisting ofat least a first and second sort of particle, comprising: a) a firstimpact area with at least one surface of at least one solid material,along which the particles of the first particle sort and the secondparticle sort of the mixture can move in such a way that at least oneportion of their particle surface is at least sectionally in contactwith the solid material surface as they move along the at least onesolid material surface; and b) a second impact area subsequent to thefirst impact area, with a first electrode area and a second electrodearea, between which an electrical voltage can be applied; and with afirst accumulation area for particles of the first sort and anaccumulation area for particles of the second sort separate from thefirst accumulation area, wherein the at least one surface of the atleast one solid material is concave in the first impact area, so thatthe particles of the first sort and second sort that can move along theconcave surface are pressed against the concave surface of the solidmaterial as a result of their centrifugal force as they move inside thefirst impact area; wherein the first impact area has a curved channelwith a first end and a second end, in which a product inlet and fluidinlet is connected to the first end, and a product separator with aproduct outlet and fluid outlet is secured to the second end forseparating the product and fluid, wherein the mixture having particlesof the first sort and particles of the second sort can be suppliedthrough the product inlet, carried by a fluid stream supplied throughthe fluid inlet and discharged through the fluid outlet through thefirst impact area with the curved channel and along its concave surface,and finally routed through the product separator and its product outletinto the second impact area with the particles in their respectiveelectrically charged state.
 2. The device according to claim 1; whereinthe first impact area is designed as a cyclone separator with a fluidinlet, an fluid outlet, a product inlet and a product outlet.
 3. Thedevice according to claim 1; wherein said device has a supply areathrough which the mixture having particles of the first sort andparticles of the second sort can be supplied to the first impact area bymeans of a conveying device in the supply area via the product inlet. 4.The device according to claim 1; wherein the first impact area haspivoted in a casing a rotor element, which is shaped in such a way that,when turned, the particles of the mixture contained in the first impactarea can be accelerated through the surface of the rotating rotorelement with a radial and tangential component, and relayed to theconcave inner surface of the casing at a velocity with a radial andtangential component.
 5. The device according to claim 4; whereinelevations project into a gap area between the rotor element and casingthrough which can pass the moving particle current, and extend from thesurface of the rotor element and/or from the inner wall of the casing,so that any agglomerates that might be contained in the mixture aredispersed before it is routed to the concave inner surface.
 6. Thedevice according to claim 1; wherein the first impact area is designedas a centrifugal device, and the rotor element is an impact plate withnumerous elevations.
 7. The device according to claim 6; wherein aproduct inlet is arranged at a location of the casing that is eccentricrelative to the impact plate, so that loading takes place eccentricallyon the impact plate in the casing.
 8. The device according to claim 4;wherein an air pump or a compressor is hooked up to the first impactarea in order to pump a fluid in the first impact area countercurrentlyto the centrifugally accelerated particle current.
 9. The deviceaccording to claim 4; wherein an air pump or a compressor is hooked upto the first impact area in order to pump a fluid in the first impactarea cocurrently to the centrifugally accelerated particle current. 10.The device according to claim 4; wherein the elevations are angularelevations in the radially outer edge area of the impact plate.
 11. Thedevice according to claim 5; wherein the elevations are web-likeelevations that extend from the center to the edge area of the impactplate.
 12. The device according to claim 5; wherein all elevations areformed on the at least one impact plate.
 13. The device according toclaim 5; wherein the elevations formed on the at least one impact plateare designed as turbine blades.
 14. The device according to claim 1;wherein a dispersing angle against which the particles of the mixturetransported through the device collide during their directional reversalis arranged upstream from the curved area of the curved channel, so thatany agglomerates that might be contained in the mixture are dispersedbefore being transported further to the curved channel.
 15. The deviceaccording to claim 3; wherein the supply area of the conveying devicehas a conveyor worm with which the particles of the first sort andparticles of the second sort can be supplied to the first impact area,wherein the particles receive their final electrical charge by rubbingagainst the surface of the conveyor worm while supplying the firstpartial charge.
 16. The device according to claim 1; wherein the firstimpact area is a hammer mill or an impact crusher.
 17. The deviceaccording to claim 1; wherein the first impact area has a non-cloggingair separator or a turbo-mill.
 18. The device according to claim 1;wherein, in the second impact area, the first electrode area consists ofa first electrode, and the second electrode area consists of a secondelectrode.
 19. The device according to claim 1; wherein the firstelectrode and second electrode in the second impact area are arrangedlike a plate capacitor.
 20. The device according to claim 1; wherein thefirst electrode and second electrode in the second impact area arearranged like a cylinder capacitor.